Photographic exposure apparatus

ABSTRACT

A portable photographic exposure apparatus for making reproductions of loft drawings, body drafts or the like directly from the drawing table on which the drawing is made. A wheeled cabinet structure has a horizontal supporting surface, the height of which is adjustable to the height of a drawing table, with an exposure unit adapted to be mounted on the supporting surface and containing a light source, a set of electric motor driven wheels, and a source of static electricity. The exposure unit is driven over the drawing table to expose a sheet of film which is laid over the drawing on the drawing table to reproduce the drawing. Static electricity projected by the exposure unit presses the film firmly against the drawing to be reproduced. The electric motor is reversible to return the exposure unit to its supporting cabinet. The apparatus may also be used to expose a negative which is subsequently processed to provide positive reproductions of the loft drawing.

BACKGROUND OF THE INVENTION

1. Description of the Prior Art

In the reproduction of large metal or synthetic sheet loft drawings andbody drafts, it is customary to ship the completed drawings to a specialfacility for photographic processing to make the necessaryreproductions. Drawings of this nature are generally made on largesheets of suitably coated aluminum, synthetic sheets or the like and theshipping and handling for purposes of making reproductions is arelatively expensive process, particularly as the risk of damage and thepossibility of temperature and humidity changes may cause distortions.Portable exposure machines have been proposed heretofore, such as aredisclosed in U.S. Pat. Nos. 2,292,668; 2,550,640; 3,254,586; and3,385,192. However, such machines involve transportation problems if itis desired to use them at multiple locations, and they still do notreadily serve to maintain close contact between the film and the drawingfor accurate reproduction.

2. Field of the Invention

This invention relates to improvements in portable photographic exposureapparatus of the type generally used to expose large sheets of filmwhich are laid on large loft drawings, body drafts and the like forproduction of accurate photographic reproductions.

SUMMARY OF THE INVENTION

The present invention contemplates an improved portable exposure unitwhich can be used to make positive reproductions of drawings of thistype directly from the drawing table on which the drawing is made,thereby eliminating the expensive shipping and handling of the drawing.The film used with this apparatus may consist of commercially availablematerial such as "Mylar" or other similar dimensionally stable materialhaving a light sensitive coating thereon to provide a reproduction whenexposed over the drawing. Such film lends itself to being pinned to thedrawing by an electrostatic charge which according to the presentinvention is projected from an electrode carried directly by theexposure unit.

DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention, reference may be hadto the accompanying drawings illustrating a preferred embodiment of theinvention in which like reference characters refer to like parts throughout the several views, and in which:

FIG. 1 is a fragmentary perspective view of a drawing table having aloft drawing thereon covered by a sheet of film and showing theapparatus of the present invention being used to make a reproduction ofthe drawing;

FIG. 2 is an elevational side view of the apparatus with parts brokenaway for purposes of clarity;

FIG. 3 is an elevational view of the apparatus of FIG. 2 as seen fromthe right side thereof;

FIG. 4 is a cross sectional view taken substantially on line 4--4 ofFIG. 2;

FIG. 5 is a fragmentary perspective view of a portion of the cabinetstructure of the apparatus of FIGS. 2-4;

FIG. 6 is a bottom plan view of the exposure unit embodied in theapparatus;

FIG. 7 is a cross sectional view taken substantially on line 7--7 ofFIG. 6; and

FIG. 8 is a fragmentary perspective view of a portion of the exposureunit of FIGS. 6 and 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 through 4 illustrate a drawing table 10 including a supportingleg 12 and having a loft drawing 14 thereon. The table 10 may be ofconventional construction and the loft drawing 14 consists of a largemetal or synthetic sheet of the kind conventionally used for makingdrawings of this type. A sheet of film 15 to be exposed covers at leastthe main portion of the drawing 14.

The apparatus of the present invention includes a cabinet structureindicated generally at 16 and comprising a lower carriage unit 18 and arectangular cabinet 20. The carriage 18 comprises a rectangularframework 22 having vertical corner posts 24 and casters 26 for movingthe unit 16 into position at one end of a drawing table as shown inFIGS. 1 and 3. The cabinet includes an upper horizontal supportingplatform 28 on which the exposure unit 30 is normally carried. Thesupporting platform 28 may overextend the ends of the cabinet 20 asshown in FIGS. 1 and 4 and the phantom lines of FIG. 2, or may besubstantially the length of the cabinet 20 as in the solid lines of FIG.2, to carry an exposure unit 30 of any desired length, depending uponthe size of the drawing to be reproduced.

As shown in FIGS. 4 and 5, the framework 22 of the carriage 18 has fourvertically extending racks 32 secured thereto and extending upwardlywithin the side walls 34 of the cabinet unit 20. The corners 35 of thecabinet 20 nest within the vertical corner posts 24 of the carriage 18.A shaft 36 is rotatably journaled in the end walls 34 of the cabinet,and a hand wheel 38 is secured to one end of the shaft 36 exteriorly ofthe cabinet. A worm 40 meshes with a gear 42 secured on a shaft 44supported by brackets 46 on the inner sides of the walls 34. At theirouter ends the shafts 44 carry pinions 48, each of which meshes with oneof the racks 32 so that upon rotation of shaft 36 by the hand wheel 38the entire cabinet unit 20 will be raised or lowered so that the heightof the platform 28 may be made level with the table 10.

The exposure unit 30, shown in detail in FIGS. 6-8, 50 comprises agenerally rectangular box-like structure having side walls 52 and a topwall 56, leaving the bottom open, and is adapted to contain a series offluorescent tube lights 58 which extend substantially throughout thelength of the unit. An additional tube light 60 is disposed above andextends transversely across the lights 58 at each end of the unit toinsure sufficient and substantially uniform lighting for proper exposureof the film. A pair of axles 62 are mounted in brackets 64 secured tothe under side of the top wall 56 and carry the wheels 66 on which theexposure unit may be moved from the platform 28 across the drawing tableand returned. As seen in FIGS. 3 and 6, one of the axles 62 has a bevelgear 68 secured thereto and meshed with a bevel gear 70 having a driveshaft 71 extending upwardly therefrom and journaled in the top wall 56so as to be driven from an electric motor 72 mounted thereon. The motor72 is preferably reversible and a suitable speed reduction may beprovided between the motor 72 and the wheels 66 to propel the exposureunit 30 at the proper speed for correct exposure of the film ornegative. A power cable 102 for supplying current to the motor 72extends from the exposure unit 30 to the cabinet 20 on which it may becoiled when the unit is not in use.

The exposure unit 30 is provided with a motor driven fan 74 which isadapted to discharge cooling air downwardly through an opening 78 in thetop wall 56 over which the fan is disposed. A baffle structure 80 isadapted to direct the cooling air over the lights 58 to prevent theiroverheating.

At the leading edge of the exposure unit 30 a housing 82 having an openbottom carries an electrostatic discharge electrode 84 electricallyconnected to an electrostatic control unit 86 mounted in the cabinet 20.The electrode 84 has a series of depending discharge pins 88 which, whenthe electrode 84 is energized, will discharge an electrostatic fluxfield along the entire leading edge of the exposure unit in advance ofthe leading wheels 66 to produce an electrostatic charge between thefilm 15 and the drawing 14 so the film will be firmly pressed down andsmoothed against the drawing to be reproduced to insure accurateexposure of the film. In the case of a synthetic material drawing, theelectrostatic charge also serves to flatten the drawing 14 to thesurface of the drawing table 10.

At its forward lower edge the housing 82 carries a wiper pad 90 made offelt or other suitable material. The pad 90 is sufficiently weighted tofirmly engage the film as the exposure unit travels over the film topress out any air pockets that may exist between the film and theunderlying drawing prior to their exposure to the electrostaticdischarge. The pad 90 may be pivotally mounted along the leading edge ofthe housing 82, as shown in FIG. 8, and a handle 92 on a pivot pin 93 isprovided for lifting the pad 90 at the beginning of an operation so thatit can be placed on top of the edge of the film which is first traversedby the exposure unit 30. Another pad 94 of felt or other suitablematerial extends along the trailing edge of the exposure unit andfunctions to dissipate the electrostatic charge after exposure of thefilm has taken place to facilitate separation of the film from thedrawing.

An electrical conductor 96 in the form of a metal strap may be hookedover one edge of the drawing table 10 to engage the loft drawing 14 asshown in FIGS. 1 and 3. The conductor 96 is connected by a ground wire98 to a piece of metal, such as the handle 100 on the cabinet 20, toground the sheet of metal comprising the loft drawing as well as thedrawing table 10, to direct the electrostatic flux field from theelectrode 84 toward the drawing 14 and the table 10.

By means of the apparatus described it is possible to make positivereproductions of loft drawings directly from a drawing table withoutrequiring any handling of the loft drawings. The apparatus may easily bemoved from one drawing to the next in a drafting room to successivelymake reproductions from the drawings on all of the drawing tables.

It is possible to make positive reproductions in the manner describedunder normal lighting conditions. However, it may be advisable undersome conditions to block out the film from exposure to the normallighting in a drafting room and this may readily be accomplished bypartially unrolling a roll of opaque cloth (not shown) to cover the filmwith the roll carried or engaged by the leading edge of the exposureunit so that the cloth will be rolled up as the unit traverses the film.Similarly, a roll or length of such opaque cloth (not shown) may beattached to the trailing edge of the exposure unit to progressivelycover the exposed portion of the film.

The apparatus has been described in connection with the reproduction ofpositives from suitably coated film which is commercially available. Itwill be apparent that the apparatus could also be used to make negativesrather than positive reproductions, although in making negatives fromthe original loft drawings in the manner described it would be necessaryto carry out such process under controlled lighting conditions.

The electrical controls for the exposure unit 30 may be mounted in anyconvenient place, either on the exposure unit itself or within thecabinet 20. The power cable 102, shown in FIG. 1, may extend from theexposure unit 30 to suitable control units, as indicated at 104 in FIG.3, for the various electrical units of the apparatus. A power line 106shown in FIG. 2 is adapted to be plugged into a conventional source ofelectrical power and supplies current to the apparatus.

What I claim as my invention is:
 1. Exposure apparatus for making aphotographic reproduction of a loft drawing or the like supportablyoverlying a horizontal drawing table surface, comprising a box-like.[.structure.]. .Iadd.unit .Iaddend.having an open bottom and containinga light source, a set of wheels on said .[.structure.]. .Iadd.unit.Iaddend.on which same is movable over a sheet of light sensitiveexposure film covering the drawing to be reproduced, an electrostaticdischarge means extending along the leading edge of said exposure unitand constructed to direct an electrostatic charge toward said film anddrawing to thereby adhere the film horizontally and smoothly to thedrawing as said exposure unit moves thereover to expose said film, amotor for driving said wheels to propel said exposure unit over saidfilm, means for electrically grounding the drawing, and control meansfor energizing said light source, said motor and said electrostaticdischarge means.
 2. Apparatus according to claim 1 wherein saidelectrostatic discharge means comprises an electrode extending along theleading edge of said exposure unit and having a series of spaced,downwardly extending discharge pins thereon.
 3. Apparatus according toclaim 1 including means extending along the trailing edge of saidexposure unit for dissipating the electrostatic charge between thedrawing and the exposed film.
 4. Apparatus for photographically exposingfilm overlying a loft drawing or the like, comprising a housing havingexposure lighting means, means moving said housing and said drawing withthe overlying film relative to each other in close juxtaposition forprogressive exposure of said film, .[.and.]. said housing carrying anelongated electrostatic discharge means ahead of said lighting means forprogressively directing an electrostatic flux field to said film anddrawing to adhere same together during exposure, and means forprogressively dissipating electrostatic charge from said film anddrawing following exposure to facilitate separation of said film fromsaid drawing.
 5. The apparatus as defined in claim 4 and in which saiddrawing and film are supported flat on a drawing table surface, and saidmeans moving said housing comprises means driving same over the surfaceof said table from one end to the other of said drawing.
 6. Theapparatus as defined in claim 4 and in which said housing comprises abox-like structure having an open bottom of a length to overextend thewidth of said film, said lighting means being carried in said housingand adapted to direct exposure light from the open bottom onto said filmimmediately subsequent to electrostatic adherence thereof to saiddrawing as said housing is moved thereover. .Iadd.
 7. Exposure apparatusfor making a photographic reproduction of a loft drawing or the likesupportably overlying a horizontal drawing table surface, comprising abox-like unit having an open bottom and containing a light source, a setof wheels on said unit on which it is movable over a sheet of lightsensitive exposure film covering the drawing to be reproduced, a meansfor applying a downward force proximate the leading edge of saidexposure unit and adapted to apply such force toward said film anddrawing to cause the film horizontally and smoothly to adhere to thedrawing as said exposure unit moves thereover to expose said film, and amotor for driving said wheels to propel said exposure unit over saidfilm. .Iaddend..Iadd.
 8. The combination as set forth in claim 7 whereinsaid downward force applying means is spaced forwardly of theforwardmost of said set of wheels and a means is operably connected tosaid downward force applying means for interrupting the downwardlyapplied force from said film and drawing subsequent to passage of saidexposure unit. .Iaddend..Iadd.
 9. The combination as set forth in claim8 wherein said downward force applying means comprises an electrostaticdischarge electrode supported forwardly of said unit and wherein saidmeans for dissipating said charge comprises a pad of electricalinsulating material for dissipating such charge. .Iaddend..Iadd.
 10. Thecombination as set forth in claim 9 wherein there is further positionedat the forward edge of said unit a wiper member weighted to engage thefilm and drawing and to press out in advance any air pockets that mayexist therebetween. .Iaddend. .Iadd.
 11. The combination as set forth inclaim 10 wherein said exposure unit includes a plurality of longitudinallight tubes extending transversely relative to the path of movement ofsaid unit. .Iaddend..Iadd.
 12. Exposure apparatus for making aphotographic reproduction of a loft drawing or the like supportablyoverlying a horizontal drawing table surface, comprising a box-like unithaving an open bottom and containing a light source, a plurality ofwheels on said unit on which it is movable over the surface of a sheetof light sensitive exposure film covering the drawing to be reproduced,means for providing a downward force along the leading edge of saidexposure unit to cause the film and drawing to be pressed together andto the drawing table surface, a motor for driving the said wheels topropel said exposure unit over said film, and variable speed controlsoperatively connected to and controlling the operation of said motor forcontrolling the exposure time of the apparatus. .Iaddend. .Iadd. 13.Exposure apparatus for making a photographic reproduction of a loftdrawing or the like supportably overlying a horizontal drawing tablesurface, comprising a box-like unit having an open bottom and containinga light source, a plurality of wheels on said unit on which it ismovable over the surface of a sheet of light sensitive exposure filmcovering the drawing to be reproduced, means for providing a force alongthe leading edge of said exposure unit to cause the film and drawing tobe pressed together and to the drawing table surface, a motor fordriving the said wheels to propel said exposure unit over said film, andvariable speed controls operatively connected to and controlling theoperation of said motor for controlling the exposure time of theapparatus. .Iaddend..Iadd.
 14. Exposure apparatus for making aphotographic reproduction of a loft drawing or the like supportablyoverlying a horizontal drawing table surface, comprising a box-like unithaving an open bottom and containing a light source, a plurality ofwheels on said unit on which it is movable over the surface of a sheetof light sensitive exposure film covering the drawing to be reproduced,means for providing a force to cause the film and drawing to be pressedtogether and to the drawing table surface, a motor for driving the saidwheels to propel said exposure unit over said film, and variable speedcontrols operatively connected to and controlling the operation of saidmotor thus controlling the exposure time of the apparatus. .Iaddend.